KR101405845B1 - Method for manufacturing of valve train parts using with metal powder injection molding - Google Patents

Abstract

The present invention relates to a method for manufacturing a valve train component using a metal powder injection molding method, the method comprising the steps of: mixing a metal powder and a binder to obtain a raw material for injection molding; Injecting the obtained injection molding raw material into a mold having a valve train component shape to form a molded body; Solvent extraction of the formed body; Degassing and sintering the solvent-extracted shaped body to form a sintered body; Sizing the formed sintered body; Subjecting the sizing sintered body to a vacuum carburizing treatment; And polishing the sintered body subjected to the vacuum carburization treatment; To a method of manufacturing a valve train component using metal powder injection molding.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for manufacturing a valve train component using metal powder injection molding,

The present invention relates to a method of manufacturing a valve train component using metal powder injection molding, and more particularly, to a method of manufacturing a valve train component by metal powder injection molding, To a method of manufacturing a valve train component using metal powder injection molding in which the physical properties are improved.

An internal combustion engine engine is a device for generating power by sucking air and fuel from the outside and burning it in a combustion chamber. The engine includes an intake valve for sucking the air and fuel into the combustion chamber, and an exhaust valve for exhausting the explosive gas burned in the combustion chamber The intake and exhaust valve is opened and closed by a camshaft rotating in conjunction with the rotation of the crankshaft.

At this time, a series of parts for operating the intake and exhaust valves, such as a drive cam, a camshaft, a tappet, a rocker arm, and a rocker arm link, are referred to as a valve train.

Meanwhile, the automobile industry is developing various eco-friendly vehicles with the target of reducing carbon dioxide emissions to 50g / km, which is 35-50% of current level, by 2020. In case of fuel economy, Average Fuel Econmomy) of 23.2 km / l (54.5 mpg).

Recently, a continuous variable valve lifter (CVVL) mechanism has been applied to maximize the fuel consumption efficiency and performance of the engine by optimizing the intake air amount by controlling the height of the intake valve according to the engine rotation speed of the vehicle have.

FIG. 1 is a perspective view showing a rocker arm, FIG. 2 is a perspective view showing a rocker arm link, FIG. 3 is a perspective view showing a structure in which a rocker arm and a rocker arm link are fastened, The rocker arm 100 and the rocker arm link 110 having a sophisticated shape as shown in the drawing operate as a part of the configuration of the continuously variable valve lifter 120. [

At this time, since the valve train components such as the rocker arm 100 and the rocker arm link 110 must be used for a long time under severe conditions, excellent durability and precision such as strength, abrasion resistance and impact resistance are required.

For this purpose, a conventional precision casting method has been used in comparison with a conventional casting method. However, since the shape of the valve train parts is precise, a large number of additional machining steps are required to achieve the final shape even after casting.

That is, in the case of manufacturing by the above-mentioned precision casting method, there is a problem that the cost of the product is greatly increased because the mechanical strength is excellent but the dimensional accuracy is poor and the process cost and material loss due to additional processing are additionally generated.

It is an object of the present invention to solve the above problems and to provide a method of manufacturing a valve train, The present invention provides a method of manufacturing a valve train component using metal powder injection molding applicable even in a severe condition such as an engine.

In order to achieve the above object, a method for manufacturing a valve train component using metal powder injection molding according to the present invention is a method for manufacturing a valve train component, which comprises mixing metal powder and a binder, ; Injecting the obtained injection molding raw material into a mold having a valve train component shape to form a molded body; Solvent extraction of the formed body; Degassing and sintering the solvent-extracted shaped body to form a sintered body; Sizing the formed sintered body; Subjecting the sizing sintered body to a vacuum carburizing treatment; And polishing the sintered body subjected to the vacuum carburization treatment; (S100), the metal powder is mixed with 93% by weight of the metal powder and 7% by weight of the binder. The metal powder may include 2% by weight of nickel (Ni), molybdenum 0.5% by weight of Mo), 0.25% by weight of carbon (C) and the balance of iron (Fe).

According to an embodiment of the present invention, it is preferable that the step of obtaining the raw material for injection molding is such that the metal powder is 93% by weight and the binder is 7% by weight.

In one embodiment of the present invention, the metal powder preferably contains 2% by weight of nickel (Ni), 0.5% by weight of molybdenum (Mo), 0.25% by weight of carbon (C) and the balance of iron (Fe).

According to an embodiment of the present invention, the step of forming the sintered body may include supplying argon gas in a vacuum atmosphere, heating the degreased shaped body to a temperature of 1250 ° C or higher, and then soaking the temperature for 2 hours desirable.

Further, the step of processing the vacuum carburization to an embodiment of the present invention, after the sizing was heated to the processed sintered body into 890 ℃ following acetylene carburizing treatment for 1 hour by using a (C ₂ H ₂₎ gas, the 890 ℃ For 10 minutes, then warmed to 820 占 폚, and then spread carbon for 20 minutes at the same temperature.

According to an embodiment of the present invention, in the vacuum carburizing step, the carbon-diffused sintered body is quenched by using an oil bath at a temperature of 80 ° C., heated to 180 ° C. and held for 90 minutes It is preferable to further perform a cooling tempering.

Further, in an embodiment of the present invention, it is more preferable that the valve train component is a rocker arm or a rocker arm link.

The effect of the present invention having the above-described structure can be achieved by replacing the conventional precision casting method with a metal powder injection molding having excellent dimensional accuracy, thereby reducing the process cost and the material loss due to the additional processing, thereby reducing the cost.

In addition, although it is manufactured by metal powder injection molding, the carbon powder can be easily controlled by adjusting the metal powder composition and the process conditions, so that uniform carburization is possible, and the strength and surface roughness are improved. There is an advantage to be secured.

1 is a perspective view of the continuously variable valve lifter.
2 is a perspective view showing the rocker arm;
3 is a perspective view showing a rocker arm link;
4 is a perspective view showing a structure in which a rocker arm and a rocker arm link are engaged;
5 is a flowchart illustrating a method of manufacturing a valve train component using metal powder injection molding according to the present invention.
6 is a graph showing a degreasing and sintering process according to an embodiment of the present invention.
7 is a graph showing a vacuum carburization and quenching process according to an embodiment of the present invention.
8 is a graph showing a hardness test result of a valve train component (rocker arm) according to an embodiment of the present invention.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Conventionally, parts manufactured by precision casting satisfies the physical properties required by the valve train operating environment, but it is not excellent in dimensional accuracy, and there is a limit in the cost because of cost increase due to post-processing and material loss.

Accordingly, it is an object of the present invention to replace conventional precision casting processes involved in the manufacture of valve train components with metal powder injection molding with excellent dimensional accuracy.

Metal Powder Injection Molding (MIM) is a metal molding technology that combines powder metallurgy technology and injection molding, which is a mass production technology of precision plastic parts. In general, metal powder is mixed with fine metal powders and binder Injecting the mixture into a mold, removing the binder from the injection-molded body, and sintering only the powder to obtain a component.

Here, the metal powder injection molding generally requires better post-treatment such as improvement of physical properties by surface heat treatment, which is superior in dimensional precision as compared with precision casting but has low physical properties of the resulting product. Conventionally, It is difficult to obtain desired physical properties.

That is, despite the advantages of metal powder injection molding, there is a problem in that it is not suitable for use as a method for manufacturing a component that operates in a harsh environment such as an engine valve train.

Therefore, the object of the present invention is to obtain the effect of cost reduction by optimizing the alloy composition and the manufacturing process conditions in the metal powder injection molding to solve the above-mentioned disadvantages and to secure the excellent dimensional accuracy and to reduce the post- do.

FIG. 5 is a flowchart illustrating a method of manufacturing a valve train component using metal powder injection molding according to the present invention, which will be described in detail with reference to the following examples.

1. Mixing step (S100)

First, a metal powder and a binder are mixed to obtain a raw material for injection molding. The binder is added to maintain the flowability and shape of the metal powder during injection molding, and a conventional organic binder is used. Polyethylene, or a lubricant such as paraffin wax and stearic acid.

Specifically, raw materials for injection molding were obtained by mixing homogeneously such that the metal powder was 93% by weight and the binder was 7% by weight.

When the metal powder is less than 93% by weight, the fluidity at the time of injection is good but it takes a long time at the time of degreasing. When the metal powder is more than 93% by weight, the molded body at injection does not have sufficient strength, Do.

The metal powder is preferably mixed with molybdenum (Mo) by separately supplying each metal element. Specifically, the metal powder is mixed with carbonyl Fe (1) (containing 0.76 wt% of carbon (C)), carbonyl Fe 2) (containing 0.03% by weight of carbon (C), nickel (Ni) and molybdenum (Mo) in an amount of 2% by weight of nickel, 0.5% by weight of molybdenum, 0.25% by weight of carbon, (Fe).

In the prior art, there is a problem that carbon control is difficult due to decarburization after purchasing Fe-2wt% Ni-0.9wt% C (thin-walled / deep-walled). In contrast, the present invention provides a metal powder composition and an optimal composition of a binder Accordingly, carbon control is easy, rigidity is ensured, and carburization for curing becomes possible.

The mixing was carried out at 160 캜 for 3 hours at 30 rpm. If the temperature is lower than the above-mentioned condition or the mixing time is shortened, the binder may not be mixed as it has sufficient fluidity, If the mixing is carried out for a long period of time, the binder may be degreased during mixing, so that it is preferable to satisfy the mixing condition.

2. In the injection step S110,

The obtained injection molding raw material was injected into a mold having a valve train component shape under conditions of a nozzle temperature of 145 占 폚, an injection speed of 33 mm / s, an injection pressure of 3.5 MPa, and a mold temperature of 30 占 폚 to form a molded article.

At this time, the nozzle temperature and the mold temperature are considered in consideration of the fluidity of the raw material for injection molding and the vaporization of the binder, and the injection pressure and injection speed consider smooth injection and overloading of the injection molding apparatus.

3. Solvent extraction step (S120)

In order to shorten the degreasing time, the formed body thus formed is immersed in a n-heptane solution in advance and subjected to solvent extraction at about 40 ° C for 10 hours to 12 hours to remove most of the binder in the molded body. Respectively.

At this time, if the temperature exceeds 40 ° C, the binder removal reaction rate becomes too fast before an appropriate extraction passage is formed in the formed body, so that stress is concentrated inside the formed body, thereby generating cracks.

If the temperature is less than 40 캜, cracking does not occur, but solvent extraction requires a long time, and therefore, the process cost is increased. Therefore, it is preferable that the above condition is satisfied.

4. Degreasing and Sintering Step (S130)

6 is a graph illustrating a degreasing and sintering process according to an embodiment of the present invention.

Degreasing is a step of completely removing the binder in the formed body before sintering. In order to remove the binder remaining in the molded body after the solvent extraction, pyrolysis and degreasing were performed.

The most common method of removing the binder is to slowly evaporate the binder through pyrolysis by slowly heating the shaped body.

However, when the binder is heated and evaporated, most of the binders evaporate slowly at a low temperature, and when the binder reaches a certain temperature, the binder evaporates rapidly, resulting in distortion of the molded article such as twisting or warpage.

Accordingly, as shown in FIG. 6, vacuum pumping is performed at 25 ° C. for 10 minutes to prevent the above-mentioned problems, and then nitrogen (N ₂ ) gas is charged at a rate of 8 L / min. To remove the binder in each step, thereby minimizing the deformation of the molded body.

That is, in the initial temperature raising temperature range, passages for degreasing the binder are formed in the molded body, the low temperature binder is degreased at a middle temperature range, and degreasing is performed sequentially for the high temperature binder at a high temperature range.

Subsequently, purging was performed to make a vacuum state, argon (Ar) gas was supplied at a rate of 5 L / min, the degreased compact was heated to a temperature of 1250 ° C or higher, To form a sintered body.

During the sintering, densification and grain growth progress to consolidate the formed body. The sintering may be performed in a separate sintering furnace, but may be performed continuously after degreasing in the vacuum degreasing sintering furnace as described above.

In the past, sintering was performed at a temperature of less than 1250 占 폚 in a mixed gas atmosphere in which a hydrogen gas and a nitrogen gas were mixed. In this case, carbon in the material was uneven. In contrast, ) Is uniformized.

5. Sizing (sizing) processing step (S140)

The sintered body was subjected to sizing at a pressure of 100 kgf / cm ² to determine the dimensions of the sintered body.

6. Vacuum Carburizing Treatment Step (S150)

7 is a graph showing a vacuum carburizing and quenching process according to an embodiment of the present invention.

Was carried out as shown, about one hour carburizing treatment while using approximately 30 minutes was then carbon acetylene (C ₂ H ₂₎ as the temperature was raised during the gas to the processed sintered compact sizing said to be about 890 ℃ the carburizing temperature in a vacuum environment as shown

Then, the temperature was maintained at 890 캜 for about 10 minutes, the temperature was lowered to about 820 캜 for about 10 minutes, and the carburized carbon was diffused for a total of 40 minutes while maintaining the temperature at 820 캜 for about 20 minutes.

The carbon-diffused sintered body was then quenched at a temperature of about 80 ° C. using an oil bath to secure hardness and strength. The temperature of the sintered body was raised to about 180 ° C. for about 90 minutes to improve toughness Followed by additional cooling and tempering.

Conventionally, carbon monoxide (CO) and methane (CH ₄ ) are used as the carburizing gas, and the carbon potential is constant. Thus, there is a problem that the depth of the cured layer is different or the precure is generated. However, C ₂ H ₂ ) gas and carburized in a vacuum atmosphere to control the carbon potential pulse, a uniform layer of depth can be obtained irrespective of the thickness.

7. Polishing step (S160)

The surface of the vacuum-sintered sintered body was ground for 2 hours to smooth it.

Depth (mm) Rocker arm hardness (Hv 0.3) 0 684.9 0.05 707.1 0.1 675.4 0.2 670.7 0.3 586.3 0.4 560 0.5 557.1 0.6 529.9 0.7 475.6 One 385.3 1.5 385.3 2 395.6

8 and Table 1 are graphs and tables showing the hardness test results of valve train parts (rocker arms) according to one embodiment of the present invention.

As shown in the figure, the surface of the rocker arm 100 has a hardness of about 700 Hv, a surface hardness of about 400 Hv or more, and an effective hardening layer depth of about 0.52 mm as a result of the carburizing heat treatment. 7.6 g / cc.

As a result of various tests, the physical properties that the rocker arm 100 should have basically have a density of 7.5 g / cc, a surface hardness of 650 Hv or more, a hardness of 300 Hv or more from the surface to the deep portion, and a depth of 0.3 to 0.6 mm of the effective hardening layer. It can be seen that the rocker arm 100 according to the present invention satisfies all of the above basic conditions.

The mechanical strength of the rocker arm 100 produced by the present invention was measured. As a result, a tensile strength of 940 MPa, an elongation of 0.5%, and an impact strength of 9.1 J / cm ² were obtained. ≪ / RTI >

In addition, since the metal powder injection molding having excellent dimensional accuracy is used, the machining area is reduced by 60 to 80% compared to the conventional precision casting, thereby reducing the process cost and material loss due to the additional machining, thereby achieving cost reduction effect (Accuracy of 0.65% in the dimension accuracy of the rocker arm 100 according to the conventional precision casting method, and 0.13% in the dimension accuracy of the rocker arm 100 according to the present invention)

Rocker Arm: 100 Rocker Arm Link: 110
Continuous variable valve lifter: 120

Claims (7)

A method of manufacturing a valve train component,
Mixing the metal powder and the binder to obtain a raw material for injection molding (S100);
Forming a molded body by injecting the obtained injection molding raw material into a mold having a valve train component shape (S110);
Solvent extraction of the formed body (S120);
A step (S130) of forming a sintered body by degreasing and sintering the solvent-extracted molded body;
Sizing the formed sintered body (S140);
A step (S150) of vacuum carburizing the sintered body subjected to the sizing process; And
Polishing the sintered body subjected to the vacuum carburization (S160); / RTI >
The metal powder is mixed with 2 wt% of nickel (Ni), 0.5 wt% of molybdenum (Mo), 0.5 wt% of molybdenum (Mo), and the metal powder is mixed so that the metal powder is 93 wt% and the binder is 7 wt% %, Carbon (C) of 0.25% by weight, and the balance of iron (Fe).
delete delete The method according to claim 1,
The step of forming the sintered body (S130) comprises supplying argon gas in a vacuum atmosphere, heating the degreased molded body to a temperature of 1250 占 폚 or more, and then soaking the metal body for 2 hours Method of manufacturing valve train parts using molding.
The method according to claim 1,
The vacuum carburizing step (S150)
The sizing sintered body was heated to 890 캜 and carburized with acetylene (C ₂ H ₂ ) gas for 1 hour,
Wherein the carbon is diffused at 890 캜 for 10 minutes and then cooled to 820 캜 and carbon is diffused at the same temperature for 20 minutes, thereby producing a valve train component using the metal powder injection molding.
6. The method of claim 5,
The vacuum carburizing step (S150)
Wherein the carbon-diffused sintered body is quenched by heating in an oil bath at a temperature of 80 ° C, then heated to 180 ° C, held for 90 minutes, and then cooled to form a metal powder injection molding. A method of manufacturing a valve train component using the same.
7. The method according to any one of claims 1 and 4 to 6,
Wherein the valve train component is a rocker arm (100) or a rocker arm link (110).

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